This invention relates generally to two part stators of laminated construction such as the cores and stators used in the construction of transformers and sub-fractional horse-power electrical motors. More particularly, this invention relates to a laminated core which, due to the necessity of applying an electrical winding thereto, must consist of two separate portions which are fitted complementally together after one of the portions has received the electrical winding.
Prior constructions have been attended by disadvantages which it is the object of this invention to overcome. The known steps in constructing a laminated magnetic core from a plurality of identical, two part laminae are: (1) dividing the two-part laminae into two stacks, all of the first parts in one stack and all of the second parts in the other, (2) riveting or otherwise securing the stacks together into rigid laminated portions, (3) wrapping one portion with the requisite electrical winding, and (4) press-fitting together under high pressure.
Although the laminae of the two parts are often stamped in assembled relation simultaneously from the same piece of metal, there are nonetheless edge contortions and burrs which interfere in such a way that considerable pressure must be exerted to force the two stacks of laminations together ensuring that, once assembled, the assembled magnetic core parts will not part. The burred or contorted edges of the laminae during press-fitting causes displacement of material, called scouring, to take place. Often scouring is caused merely by the high pressures involved. The material displaced by scouring often bridges across adjacent laminae and forms cross-paths for magnetic flux causing undesirable eddy currents or displaced material accumulates between the two assembled parts and prevents surface to surface contact at some locations forming air gaps which, of course, introduces reluctance into the magnetic gap.
Also, rivetting or securing the two parts or stacks together may cause similar reluctance and eddy currents in the stacks or assembled stator.
In certain sub-fractional horsepower electrical motors, the stator comprises a ring portion and a field core portion, both laminated, the latter generally offset to one side of the ring portion. The ring portion has a circular opening therethrough, within which the rotor is adapted to rotate, and two integral substantially parallel legs extending therefrom to one side or end. At the end of the legs a core-piece, adapted to be surrounded by a field coil, is joined at each end to a respective leg. The legs and corepiece comprise the core portion of the stator.
Heretofore, many such stators had at the inside of the leg end a straight-sided recess in which a respective end of a straight-ended corepiece was press-fitted after a coil bobbin was wound with a field coil winding, the corepiece extending through an aperture through the drum of the bobbin. The corepiece ends and the mating sides of the leg recesses extended in a straight line, the lines converging outwardly at the same acute angle to the midline of the stator. Both the ring portions and legs and the corepiece each were laminated and the laminations were secured together before assembling by rivets or otherwise.
In other prior art stators the leg ends terminated in projecting rounded portions and the inside ends of the corepiece had mating rounded recesses into which the projecting leg portions were pressed after a field coil had been wound on a bobbin mounted around the corepiece.
In both these types of stators, scouring was apt to occur when the leg piece ends were force-fitted to the corepiece ends.